Preparation Of Cationic Guar Gum And Its Application In Papermaking Wet End

As a vegetable gum distilled from guar beans, guar gum is a natural, environmental friendly and water-soluble substance. At present, it is mainly used in the kind of paper with high profit margin, such as cigarette paper. It has a good performance in enhancing the strength of sheet while has a poor retention effect. The cationic guar gum derived from it by reacting with etherifying agent can increase its retention effect dramatically with its strengthening potential. Furthermore it will maintain or improve the formation of the paper.Solvent method is used for the preparation of cationic guar gum. The advantages of solvent method include high reaction efficiency, good quality of product and convenient operation etc. A proportion of water in the reaction system is beneficial, it can make guar gum swell so that the efficiency and uniformity of the reaction are improved. It was found that a ratio of water/solvent from 1.05 to 1.80 resulted in fairly high DS of the product. Alkali plays a big role in the etherification. First it is consumed as a reactant, on the other hand, it functions as a catalyst to increase the reaction rate. Additional alkali should exist in the reaction system to convert the molecule of etherifying agent into epoxy ammonium salt which has a high reaction activity. The amount of etherifying agent is another important influencing factor. We also found that there is a strong inter-reaction between etherifying agent and alkali. A ratio of alkali/etherifying agent from 1.4 to 1.6 is suitable to produce CGG with high DS. For consideration of both reaction efficiency and operation, liquor ratio about 3.1:1 is ideal. The temperature at the beginning of the reaction does not influence very much. 40-50℃ will do and too high temperature is not recommended for the alkalization of guar gum lets out heat. To achieve a given DS, higher temperature often means shorter reaction time. Reaction at high temperature as 70-80 ℃ should not last too long. Four hours is sufficient and after that ammonium base which has already boned with guar gum may lose. The DS of CGG prepared with different solvents follows: ethanol absolute> industrial alcohol> methanol, iso-propyl alcohol proved to be inoperable under the water/solvent ratio determined by the experiment. After reaction the system should adjust the pH to 7. Stirring speed is not vital for the reaction and the importance sequence of different factors is: amount of etherifying agent> amount of alkali > inter-reaction between the above two > temperature > water/solvent ratio.Application effect of cationic guar gum is affected by many factors including composition of pulp, shearing force, dosage and sort of filler etc. We did a research in the use of cationic guar gum in bleached Kraft + talc furnish. When functioning as a retention and drainage aid, a dosage of 0.05%(based on oven pulp) of CGG is suitable considering three aspects of retention, drainage and strengthening. pH value should be controlled at 7 or so. Degree of substitution no more than 0.1 is all right. A proper amount of alum could improve the retention rate. Three different additives were applied on the base of equal cost, and the effectivity in retention and drainage is the following: CGG>CPAM>CS. Besides, we also did a primary research in the use of a blend comprising of cationic guar gum, cationic starch and a certain organic acid. In another system composed of cigarette pulp and CaCOs the best drainage effect was obtained at a dosage of 0.1 % of CGG. Whether from the handsheet test or dynamic drainage jar, retention rate got the highest at a dosage of 0.07% of CGG. Because of the use of CaCOs, drainage and retention are all much better under alkalescent surrounding than acidic system. pH value of 8 is the best choice. Further more, DS no more than 0.1 is also recommended.